Volume 25, Issue 10, Pages 2270-2279 (October 2017) A Fusion Receptor as a Safety Switch, Detection, and Purification Biomarker for Adoptive Transferred T Cells  Xiuqi Wu, Bizhi Shi, Jiqin Zhang, Zhimin Shi, Shengmeng Di, Minliang Fan, Huiping Gao, Hai Wang, Jianren Gu, Hua Jiang, Zonghai Li  Molecular Therapy  Volume 25, Issue 10, Pages 2270-2279 (October 2017) DOI: 10.1016/j.ymthe.2017.06.026 Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions

Figure 1 Construction of FR806 (A) Human full-length FR and 806 epitope of human EGFR were engineered into a fusion receptor. (B) Schematic diagram of the lentiviral vectors used for the expression of FR806. EGFR-derived 21-amino acid (aa) sequence (284VRACGADSYEMEEDGVRKCKK304) including 806 epitope (287CGADSYEMEEDGVRKC302) was inserted between FR-derived signal peptide (FR SP) and the rest of human FR (FR). F2A, ribosomal skipping sequence derived from the foot and mouth disease virus; EGFP; EF1α, elongation factor 1 alpha promoter sequences. A negative control vector was designed containing EGFP only. Molecular Therapy 2017 25, 2270-2279DOI: (10.1016/j.ymthe.2017.06.026) Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions

Figure 2 FR806-Mediated Recognization and Endocytosis of CH12 in Human T Cells (A) Binding capacity of CH12 on keratinocytes (left) and HEK293T cells (right). Compared to anti-EGFR mAb C225 (cetuximab), CH12 has no affinity to human keratinocytes and HEK293T with endogenous WTEGFR expression. (B) Detection of human T cells transduced with mock or FR806 by CH12 staining. CH12 binds significantly to T cells transduced with FR806. (C) Internalization of CH12 in FR806+ T cells. FR806+ T cells were treated with saturating concentration of biotinylated CH12 and collected at the indicated time points. After intracellular staining, the time-dependent internalization of CH12 in FR806+ T cells was observed using confocal microscopy. Scale bars, 20 μM. Molecular Therapy 2017 25, 2270-2279DOI: (10.1016/j.ymthe.2017.06.026) Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions

Figure 3 In Vitro Depletion of T Cells Transduced with FR806 by CH12-MMAF (A) Time course and CH12-MMAF dose-titration assay. Mock+ or FR806+ T cells were exposed to CH12-MMAF at the indicated concentrations for 96 hr. The positive rates of GFP were monitored and 10 μg/mL CH12-MMAF was deemed sufficient for attenuation of FR806-transduced T cells. Each of the data reflect the mean ± SD of triplicates from three different donors. (B) Sorting of FR806+ T cells. FR806+ T cells (95% positive) could be sorted with biotinylated CH12 and anti-biotin microbeads. (C) Cytotoxity mediated by CH12-MMAF to sorted FR806+ T cells or untransduced T cells (UTD). UTD or sorted FR806+ T cells were exposed to CH12-MMAF at various concentrations, and cell viability assays were performed at the indicated time points. Each of the data reflect the mean ± SD of triplicates from three different donors. (D and E) Cytotoxity mediated by mAb CH12 or free MMAF to FR806+ T cells. Cell viability of UTD or sorted FR806+ T cells was shown after being treated with the indicated concentrations of mAb CH12 (D) or free MMAF (E) for 72 hr. Each of the data reflect the mean ± SD of triplicates from three different donors. (F–H) Untransduced and FR806-transduced HEK293T cells were exposed to various concentrations of CH12-MMAF (F), mAb CH12 (G), or free MMAF (H) for 72 hr followed by a cell viability assay. Each of the data points reflect the mean ± SD of triplicates. Molecular Therapy 2017 25, 2270-2279DOI: (10.1016/j.ymthe.2017.06.026) Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions

Figure 4 In Vitro Anti-tumor Activities of FR806+ CAR-T Cells (A) Lentiviral constructs used to transduce activated T cells. (B) Flow cytometry plots for anti-CD19 CAR and FR806 expression in UTD, CAR19-transduced, or CAR19-FR806-transduced T cells. (C) Similar cytotoxicity is observed with incubation of Daudi cells with CAR19 or CAR19-FR806-transduced T cells at varying effector: target (E:T) ratios for 4 hr, as determined by a standard non-radioactive cytotoxic assay. Each of the data reflect the mean ± SD of triplicates from two donors. (D) In vitro co-culture of CAR19+ or CAR19-FR806+ T cells with Daudi cells at 1:1 ratio for 24 hr have similar IFN-γ, IL-2, and TNF-α production as measured by the ELISA. Each of the data reflect the mean ± SD of triplicates from two donors. Molecular Therapy 2017 25, 2270-2279DOI: (10.1016/j.ymthe.2017.06.026) Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions

Figure 5 Detection, Isolation, and Elimination of Anti-CD19 CAR-T Cells with FR806 Co-expression (A) Diagram of the lentiviral vectors used for the expression of FR806, anti-CD19 CAR, and GFP separated by F2A sequence. (B) Flow cytometry detection of FR806, anti-CD19 CAR, and GFP in FR806-CAR19-EGFP-transduced T cells. (C) 50:50 mixing assays were performed to test the depletion of FR806-CAR19-EGFP or mock-transduced T cells treated with 10 μg/mL CH12-MMAF. Survival of GFP+ cells was measured at the indicated time points. (D) T cells transduced with FR806-CAR19-EGFP (94.3% positive) could be isolated with biotinylated CH12 and anti-biotin microbeads. (E) Percentage of surviving UTD or sorted FR806-CAR19-EGFP+ T cells was measured by cell viability assay after incubation with the indicated concentrations of CH12-MMAF for 72 hr. Each of the data reflect the mean ± SD of triplicates from three different donors. Molecular Therapy 2017 25, 2270-2279DOI: (10.1016/j.ymthe.2017.06.026) Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions

Figure 6 CH12-MMAF-Mediated Depletion of FR806+ CAR-T Cells In Vivo (A) Experimental scheme of in vivo depletion experiments. NOD/SCID mice were injected intravenously (i.v.) with 3 × 106 Daudi cells. On day 13, cyclophosphamide was administrated to deplete host lymphocytes. At 24 hr later, 3 × 107 FR806-CAR19-EGFP-transduced T cells (50% positive) were intravenously infused into NOD/SCID mice. CH12-MMAF treatment commenced with 0.1 mg doses at day 15 by i.v. injection or saline carrier for the control cohort. Mice were sacrificed at day 18. Peripheral blood, spleen, and bone marrow were sampled and the presence of human CD3+/EGFP+ T cells was analyzed. (B) The human CD3+ population was gated to determine the rate of EGFP positivity. (C) Flow cytometry analysis of the peripheral blood samples from mice treated with CH12-MMAF or saline. (D) Percentage of CD3+/EGFP+ cells in peripheral blood, spleen, and bone marrow from mice treated with CH12-MMAF or saline. n = 6. Data represent mean ± SEM of six mice per group. Molecular Therapy 2017 25, 2270-2279DOI: (10.1016/j.ymthe.2017.06.026) Copyright © 2017 The American Society of Gene and Cell Therapy Terms and Conditions